As development and demand for techniques regarding mobile equipment, electric vehicles, hybrid vehicles, power storage devices, uninterrupted power devices and the like increase, demand for secondary batteries as energy source is rapidly increasing, and the form of demand is becoming diverse as well. Therefore, a lot of researches regarding batteries consisting of secondary batteries are underway in order to respond to various needs.
Meanwhile, in a device such as an electric vehicle and a hybrid vehicle that uses a high-power high-capacity battery, it is necessary to maintain the state of insulation between the battery and the device well. That is because, unless the state of insulation of the batteries is maintained well, leakage current may occur, causing various problems. For reference, leakage current causes unexpected discharge of battery or malfunction of electronic equipment provided in the device. Further, a device such as an electric vehicle that uses a high-voltage battery may cause fatal electric shock damages to humans.
As such, in an electric vehicle or a hybrid vehicle that uses a high-voltage battery, measuring insulation resistance is very important. As a method for measuring leakage current between a high-voltage battery and a vehicle, there is a method of breaking insulation and forcing DC current to flow, but such a method has a disadvantage that insulation is broken while measuring insulation resistance. Further, another conventional insulation resistance measuring to methods connect a coupling condenser between a positive electrode terminal and a negative electrode terminal of a high-voltage battery, and a vehicle, and applies an AC signal to the coupling condenser to measure an insulation resistance component. This has a disadvantage that since a current for charging the coupling condenser and a current for discharging the coupling condenser have to pass the same circuit, circuit designing is complicated, and there are much limitations to realizing the circuit.
Thus, in measuring the insulation resistance of a high-voltage battery, it is necessary to develop a compact, light-weight and low-cost insulation resistance measuring circuit capable of measuring the insulation resistance more easily and exactly.